Prior marine engines have used water shutter valves in their exhaust passageways to prevent water from entering the engine through the exhaust passageway. Such valves are shown in U.S. Pat. Nos. 4,178,873 and 3,759,041, both assigned to the assignee of the present application. In addition, it is known to form such shutter valve members from a high temperature resistant plastic, such as Zytel, available from the Dupont Corportion. The prior shutter valves have proven generally satisfactory for use in engines having engine cooling water injected into the exhaust to cool the exhaust before reaching the shutter valve. A problem can arise, however, if the engine is operated even briefly without cooling water flow, since the engine exhaust temperatures can then reach temperatures high enough to damage the valve member.